Update site-design-powershell.md

Updated ms.date

Author: KoenZomers

docs/declarative-customization/site-design-powershell.md

@@ -1,7 +1,7 @@
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 title: SharePoint site design - PowerShell cmdlets
 description: Use PowerShell cmdlets to create, retrieve, and remove site designs and site scripts.
-ms.date: 06/05/2020
+ms.date: 09/28/2020
 localization_priority: Priority
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